Amplifier system



' Feb. 6, 1940. H. D. HINELINE AMPLIFIER SYSTEM Original Filed Aug. 30, 19:52 he t 1 Ww .Tl:

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AMPLIFIER SYSTEM Original Filed Aug. 30, 1932 7 Sheets-Sheet 2 INVENTOR AMPLIFIER SYSTEM Original Filed Aug. 50, 1952 ts-Sheet 5 4 INVENTOR.

Feb. 6, 1940.

Original Filed Aug. 30, 1932 7 Shets-Sheet 4 (Y n r H L? J]Z 6 1.29

Feb. 6, 1940. H. D.HINEL.INE I AMPLIFIER SYSTEM Original Filed Aug. 30, 1932 7 she t 5 IN VEN TOR.

Feb. 6,

H. D. HINELINE AMPLIFIER SYSTEM Original Filed Aug. 30, 1932 I l l l l!l l l l l l l l m m I TI 60 7 She ets-Sheet 6 IN V EN TOR.

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Feb. 6, 1940. I HlNEUNE 2,189,582

AMPLIFIER SYSTEM Original Filed Aug. 30, 1932 7 h et 7 v 7 i6 IN-VENTOR.

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T @FFiQi-E application. august so, 1932, Serial No. echoes henewerl August 18, 1932? ,J tion of measurement, nor afiect the reading chtamed. For another object, is has the measure ment or small values oi alternating current and voltage which otherwise require elaborate and delicate devices for the evaluation thereof. For still other objects it has the measurement of watts, particularly small values thereof at varying frequencies, the direct measurement of volt amperes, especially in single phase circuits, the measurement of frequency, phase displacement, etc. It also has for objects the measurement of the altitude of aerial navigational devices, the amplification of small current and voltage values for the control of physical regulating devices, as well as amplification of electrical fluctuations in general.

In the art of the measurement of the various electrical units of energy satisfactory instruments have been devised for the measurement of all values of the various direct current units and for the measurement of substantial amounts of the units of alternating current. Much difllculty has however been encountered in the measurement of small values of alternating current, voltage, wattage,'and of certain of the more complex units. This dimculty occurs because of the fact that substantial amounts of current are required, when the currents are alternating, to provide alternating magnetic fields of sumcient strength to develop the necessary torque for moving an indicating pointer. Many attempts have been made to reduce the torque required but with relatively little success.

It has also been suggested that the alternating current be amplified, before being measured, by the well-known triode vacuum tube. This however has not been previously practicable because of the instability of the vacuum tube and the changes in its operation which occur with a. change of current in the energizing power supplies.

My invention provides means for the utilization of vacuum tubes for the measurement of alternating currents or small electrical values of any oi the various units and means for compensating for the change in operation of the vacuum, tube with change in value of the energizing power supply thereto. My invention further utilizes a simple, inexpensive, accurate direct current meter for the indication of the value of the alterhating current to be measured. 1 thus utilize the vacuum tube as an amplifying and converting means whereby a given value or electric current energy is converted into a much larger proportionate value of direct current energy, independently of power supply changes, which is conveniently, accurately, and easily measured by the simple inexpensive meter.

This I do by providing two similar vacuum tubes, connected in sequence, and with a power supply, such that current flows through the electron streams of the tubes in series. I further connect a. simple direct current meter, which may conveniently be of the DArsonval type, between the midpoint of the power supply and the point of connection between the successive tubes, and apply the current to be measured to the grid of one of the tubes, for the simple measurements, and to both grids for various of the more complex units.

It is well known the slope of the characteristic curve of the triode vacuum tube showing the changes in plate current with respect to grid voltage is substantially constant over a. considerablev range of plate voltages and that likewise the slope of this curve is unaffected by changes in filament-current, and filament-temperature, for a. substantial range, as long as the filamentcurrent does not fall below a minimum value. The device of my invention utilizes the properties of one vacuum tube to compensate the irregularities in another produced by changes in the power supply. The current to be measured is then applied to the tubes and a differential current obtained which is caused to energize the meter.

By various adaptations of the device of my invention, I am enabled to measure millivolts at any frequency, milliamperes at any frequency, or higher values of either, microamperes or microvolts at any frequency, watts or milliwatts displacement by a simple adaptation of my system.

And especially in the construction of amplifier systems, dimculty has been encountered in producing a single amplifier device which will amplify all of the audible frequencies and those adjacent in the sub-audible and super-audible ranges; and also in coupling a light sensitive cell to an amplifier, to secure maximum efficiency of transfer of vibrations from the cell to the amplifier system An object of this invention is to amplify uniformly a maximum range of frequencies.

Another object is to amplify uniformly a range of frequencies greater than the audible range.

Still another object is to amplify uniformly vibration frequencies below audibility and extending over the audible range.

A further object is to couple amplifier tubes in cascade with direct conductive connections from plate to grid of successive tubes.

A still further object is to couple vacuum tube amplifier members in cascade for distortionless amplification without the use of bias upon the grids.

Another object is to couple a light sensitive cell to an amplifier system by a direct conductive connection for high efliciency.

Another object is to supply a cascade amplifier and light sensitive cell from a single power source, with direct conductive connection between the various members.

Another object is to couple a light sensitive cell by direct conductive connections to a plurality of amplifier members.

This application is a continuation in part of my co-pending application Serial #394,596, filed September 23, 1929.

In the development of the art of vacuum tube amplification, attempts have been made to construct systems suitable for amplification at subaudible frequencies, such as variations occurring at one or two per second, or per minute, or per hour. Previously such systems have however required separate power supply systems for each amplifier stage, or elaborate and complicated compensation devices to prevent interaction between successive stages of such type as to render the system inoperative. Likewise, previous systems for coupling a light sensitive cell to an amplifier by direct conductive connection have been found to be incapable of distortionless operation, and of such low efflciency as to be commercially worthless. (See the articles by Kunz in the Physical Review, Vol. X, #2, pgs. 205 to 206, August 1917, and Pike in the Physical Review, Vol. XIII, #2, pgs. 102 to 108, February 1919.)

The invention hereafter claimed in this application for patent provides a direct coupled cascade amplifier, of any desired number of stages, which has no limiting lower frequency, and is operative to any frequency at which the tubes utilized will operate. The invention further provides a coupling for a light sensitive cell to an amplifier which covers the same range of frequencies. and gives a higher efficiency of transfer, and a higher output, to the amplifier system. The system is particularly adapted to high quality amplification without bias upon the grids of the amplifier tubes.

The system of this invention provides a com bination of vacuum tubes and a resistance network of such character that the potential gradient established between successive points in the network corresponds to the voltage drop in the successive tubes, and sets the potential of the respective grids at the desired value. The system further provides a power supply for a light sensitive cell, and simple means for a direct conductive connection between the input grid of the amplifier and the cell, adapted to determine the potential of the connected grid. It also provides simple means for boosting the input to the connected grid.

Other objects and structural details of the device of this invention will be apparent from the following description, when read in connection with the accompanying drawing; wherein Fig. 1 isa diagrammatic representation of circuits and apparatus embodying a simple form of my invention;

Fig. 2 is a family of characteristic triode curves of change of plate current with change of grid voltage for various plate voltages;

Fig. 31s a family of characteristic triode curves of change of plate current with change of grid voltage for various values of filament current;

Fig. 4 is an embodiment of my invention utilizing separately rectified alternating current for the power supply;

Fig. 5 is a simple form of my invention utilizing batteries for power supply;

Fig. 6 is a-form of my invention utilizing auxiliary vacuum tubes for preliminary amplification for measurement of very small values;

Fig. 7 shows an embodiment of my invention utilized as a watt meter;

Fig. 8 shows an embodiment utilized as a voltampere meter;

Fig. 9 shows an embodiment for the measure-.

ment and direct indication of frequency;

Fig. 10 shows an embodiment for the measurement of phase displacement or synchronism;

Fig. 11 shows an embodiment including a phase displacement meter for measuring the altitude of an aerial vehicle.

Fig. 12 shows a thermo-couple meter adapted to the direct operation of dampers, fuel valves, etc.;

Fig. 13 shows an adaptation of the thermocouple meter amplifier to radio signal detection and amplification,

Figure 14 is a diagrammatic representation of the circuits and apparatus of an embodiment of this invention,

Figure 15 is an alternative embodiment showing a method of connecting a light sensitive cell to a single amplifier vacuum tube, and

Figure 16 is an alternative embodiment of Fig. 2.

Referring to Fig. 1 which shows a simple embodiment of my invention, I provide triode vacuum tubes i and 2 having grid circuits 3 and 4, a transformer 5 and a. direct current meter 6. The transformer 6 has a primary coil I, a main secondary coil 8 having a mid tap, and an auxiliary secondary coil 9, insulated from coil I, and another auxiliary coil i0, connected to the coil I. The filament of the triode i is connected to the auxiliary secondary coil 9, and the filament of the triode 2 is connected to the auxiliary seca in) escapee :3.

secondary. A midpoint tap is provided at the midpoint of the secondary 8 and the meter 8 is connected to the, junction between the plate of the triode 2 and the filament circuit of the triode l. The meter 5 may be an indicating meter of the simple D'Arsonval type or may be of any more elaborate type desired, such as a recording meter, or contact making meter, relay, or other forms. The grid circuits of both trlodes l and 2 a provided with grid condensers ii and i2 and rlo leeks 1e and it. for the production of sub- 'antially equsl biases on the grids of the respec 'e tubes. One of the grid circuits, which may ably be that of trlcrle 2, is provided with u. rect connection ii) from the condenser to the ext oi rit so that no fluctuating current is re ed upon the grid to which it is connected. other clrc t "or tried with a meter oiluli'lt l "J and input terminals which are adapt ed to be connected to the source of the current which it is desired to measure. current to be measured is then passe rough the meter shunt one end of the 1 may be connected. to the filament circuit 0" e trlode l. and the other end of the shunt connected to the coudenser ii as indicated.

In the operation of this em nent of my device, an energizing power is willed through the primary coll of the tl'ansrormer S by connection to any convenient source of alternating current power. elternating potential is accordingly developed the secondaries of the transformer The potential in the coil e circulates 2. current through the filament of the triode l. heating to an electron emitting temp-rature, and the potential in the coil lll clrcu lates a current through the filament of the triode heating it also to an electron emitting temperature. The potential across the main secondary 8 of the transformer is of course alternating. When the upper end, connected to the plate of the triode l is positive, the potential causes a flow of current through the triodes l and 2 in series.

If the impedances of the two triodes are substantially the same, no potential difference will exist between the junction point of the filament to plate circuits between the trlodes and the midpoint tap on the secondary 3 of the transformer 5, and accordingly no current will flow through the meter which is connected between these points.

This condition of equality is readily obtained by adjustment of the respectivegrid leaks It and I5. Upon the passage of current through the meter shunt I! from the terminals I8, 9. potential is impressed through the condenser ll upon the grid of the trlode l. The well known rectifying action produced by the application of alternating potentials to the grid of a trlode equipped with grid leak and grid condenser then occurs, changing the grid potential and impedance of the triode I, and producing a condition of unbalance,

resulting in the passage of current through the meter 6 and the production of a meter indication which is proportional to the alternating potential developed between the terminals of the meter shunt I1 and applied to the grid of the trlode I. The current flowing through the meter 6 is then equal to the change in current which would be produced in a single triode under the usual conditions by the same applied grid voltage.

The ordinary triode is, however, very sensitive to changes in the energizing power and if a. single one is used alone the changes in plate current produced by the application of an alternating potential to the grid may be entirely obscured by sea in the value of the ener power.

The change of plate current in e. trlode with change in plate voltage is indicated in the family of curves of Fig. 2. These curves are plotted to e ow the change in plate current with change in grid voltage, and the successively higher positions of the successive curves correspond to successively increasing plate volteges. These curves show that while the actual plate current changes by a considerable amount. the rete of change per volt change upon the grid is substantially the same along the middle of curves over e considerable range of plate voltages. Accordingly, if 5W1: triodes are connected as previously disclosed, e M change in plat-e voltage a change in total current flowing therethrough. lice trio are, how-ever. symmetrical and according-y change in voltage produces an equal tn the current flowing through the two trlode and accordingly no indication on the ccmlectemeter. Likewise since giver: change in u. bias produces the some in plate current in one tube, irrespective of the ectuel Cllll' flowing. as given potential impressed upon the gril one of the trlodes will result in the some shape.

in mete ding. since the meter indicates only the di in current between the two trio-c:

slon, and accordingly a reduction in plate cullfiill. 1-57) Within certain limits, however, the reduction n plate current does not change the slope of the characteristic curve and accordingly the change in plate current per volt applied to the grid is independent of the filament current. As before, since the triodes are symmetrical, a change in plate current in one caused by a change of tilement current and temperature is compensated for by an equal change in the other, and again only the relative change produced by potential upon the grid of one, appears as a reading in the meter.

By this construction, the system becomes independent of variations in the energizing power supply over a. considerable range, a range much greater than the variations ordinarily encountered in a commercial power supply. Accord ingly the device functions smoothly and accurately without any necessity for a. correction for power supply variations. The criterion for the accuracy of the reading then becomes the accuracy with which the tube electrodes retain their relative positions, and the permanence of the grid leak resistors.

The self rectifying construction shown in Fig. 1 is usable only in the event that a very substantial difference in frequency exists between the measured current and the power current, since otherwise troublesome heterodyning effects occur. The operation is satisfactory in instances where a power frequency of 133 to 150 cycles is available, and the current to be measured has a frequency of cycles, or when the energizing power is cycles, and radio frequency values are measured.

To overcome this limitation the power supply W3 may be separately rectified by means of the construction shown in Fig. 4. In this construction triodes I and 2 are provided as in Fig. 1 with grid input circuits 3 and 4, a power transformer I having a primary coil 1 and a main secondary coil 8 as well as an indicating meter 6, as previously described. The grid circuits may contain grid condensers II and I2 as previously described, with grid leaks I4 and II. The triode 2 is provided as before with a direct connection I8 from the grid condenser to the filament circuit, and the triode I is provided with a meter shunt I1 connected between the grid condenser I I and the filament circuit, and having input leads I8 adapted to be connected to the circuit upon which the measurements are to be made. The triodes I and 2 are connected in series as in the embodiment of Fig. 1 and in the essential details the construction so far described corresponds to that of Fig. 1. The power supply is however passed through rectifier tubes 2| and 22. Auxiliary secondary coils are provided in the transformer i for heating the filaments. One of the auxiliary secondary coils 28 is connected to the filament of the rectifier tube 2| for heating it to an electron emitting temperature. Another auxiliary secondary 24 is provided for heating the filament of the triode I. This secondary 24 corresponds to the auxiliary secondary 8 of Fig. l. A third auxiliary secondary 25 is provided for heating the filament of the triode 2, and a fourth auxiliary coil 28 is provided for heating the filament of the rectifier tube 22.

The upper terminal of the coil 8 is connected to the plate of the rectifier tube 2 I. The filament circuit of this tube is serially connected to the plate of the triode I, through a filter choke 21, which desirably consists of a coil and an iron core in the fashion well known in the prior art. The triode I is further serially connected to the triode 2 through a second filter choke 28 which is desirably similar to the choke 21. The filament circuit of the triode 2 is serially connected to the plate of the rectifying tube 22 and the filament circuit of this tube is connected through ,the coil 28 to the terminal of the main secondary 8. This provides a symmetrical series circuit for the four tubes and the secondary 8. The secondary 8 is desirably adjusted in size and number of turns according to the turns in the coil 1, the power supply voltage, the voltage drop in the tubes 2| and 22, and the optimum voltage for the triodes I and 2. This will vary according to the characteristics of both the rectifier tubes and of the triodes. The meter is connected, as before, to the midpoint of the coil 8 and the Junction point on the circuit between the triodes I and 2. This preferably lies also between the filter chokes 21 and 28 in order to minimize the pulsating current fiow through the meter 6. In order to obtain a maximum smoothness and accuracy, it is further desirable that smoothing condensers 29 and 38 be connected with the filter chokes 21 and 28. The choke 28 is desirably connected to a point between the rectifier tube 2I and the choke 21, and the mid-point of the coil 8, while the condenser 30 is desirably connected between the filament circuit oi. the triode 2 and the mid-point of the coil 8. By this construction, a power supply to the triodes I and 2 is provided which is substantially free from cyclic pulsations, and at the same time connection points between the primary energy supply and the mid-point of the triode circuit, for the connection of the indicating meter are conamass:

veniently available. This construction, as before, is practicallycompletely free from any influence of change of power supply voltage, and it indicates the measured value in a manner strictly analogous to the construction shown in Fig. 1.

It is not of course necessary that an alternating power supply current be-used. A direct current supply of any convenient type may be used, as shown in Fig. 5, in which similar numbers indicate similar parts with Fig. 1, which parts perform similar functions. In addition, battery supplies are provided, as indicated, with a mid-point tap for the meter 8. Alternatively. a commercial direct current circuit may be used for the plate power supply. This circuit should desirably provide at least 220 volts of direct current. The mid-point tap for the meter may then be provided by a mid-point connection to a po-- tentiometer resistance connected across the mains, which in turn are respectively connected to the plate of the triode I, and the filament of the triode. The filaments may desirably be heated by auxiliary batteries, or they may be heated by a portion of the drop across a ballast resistance in a fashion which will be obvious to one skilled in the art, the ballast resistance being connected directly across the power mains, the filament current for the triode I then being taken from a point near the center of the ballast resistance, and the filament current for the triode 2 being taken from a portion near the end of the ballast resistance. It is of course obvious that in this embodiment a portion of the current change does not go through the meter but is wasted in the ballast resistance.

The embodiment shown in Fig. 4 may desirably utilize for the triodes I and 2, some of the higher quality triodes, preferably those which have a plate current of from to 50 milli-amperes at plate voltages of 150 to 350 volts. With tubes of this size incorporated in the device, a change in plate current of 10 milli-amperes is readily obtained by the application of an alternating current potential through the grid condensers II, to the grid of the triode I. The meter 6 is readily made to give a full scale defiection upon a total current of 10 milli-amperes, especially since in this embodiment a relatively high voltage drop is obtainable. The full scale deflection is readily obtainable with an alternating voltage drop between the grid condensers and the filament circuit having a R. M. 8. value of from 50 to 300 millivolts. This range is within the practical commercial range for meter shunts.

In some instances it may be found desirable to measure an alternating current of such small value that a voltage drop of this magnitude is unobtainable therefrom. For this purpose, the embodiment shown in Fig. 6 may be utilized. In this embodiment similar numbers represent similar parts with the embodiment shown in Fig. 4, which parts perform similar functions. It is closely similar to that embodiment except that the current to be measured is amplified before being applied to the measuring triodes. Triodes I and 2 are provided as before, supplied from a transformer 5 and connected to an indicating meter 6. The transformer has a primary 1 and secondaries 8, 23, 24, and 28. Rectifier triodes 2i and 22 are likewise provided and connected through filter chokes 21 and 28 to the triodes I and 2, in parallel with filter condensers 28 and 80. Grid condensers I I and I2 are provided in the grid circuits of the triodes I and 2 areaeea and also grid leaks It and I of suitable value to cause the well known grid leak and grid condenser detecting action to occur in the triodes. amplifier triodes 3i and 52 are likewise provided and simultaneously supplied from the secondary B of the transformer 5 from the rectifier tubes 2i and 22, in parallel with the triodes I and 2. The triodes 3i and 32 may desirably be a smaller type of triode than the type utilized for the tubes I andfi, and may desirably be of the type adapted to take a plate current of 5 to 8 milliamperes at a plate potential of 90 volts. The triodes 3| and 32 are supplied with plate current in parallel with the triods I and 2 through resistances 33 and as, which serve as amplifier resistances, and take up a portion of the voltage supplied from the rectifiers 2| and 22. The resistances 88 and 36 are desirably closely similar, and may desirably have a value of about 4,000 to 10,000 ohms. The filaments of the triodes 3i and 82 are desirably supplied with current in parallel with the filaments of the triodes I' and 2, and the filament current may, if desired, be regulated by auxiliary filament resistances, inserted in the filament circuit in the manner well known in the art. A meter shunt II is provided, similar to that in the previously described embodiments and connected by the leads I8 to the source of current to be measured. The voltage drop from the meter shunt I! may be applied to the grids of the triodes 8| and 82 in either one of two different ways. Grid condensers and 86 may be provided with grid leaks 81 and 38, of a value suitable to bias the grids to a point near the middle of the slope of the characteristic curve to obtain good accuracy of reproduction in the output circuits. Alternatively, the grid condensers and grid leaks may be dispensed with and the grid of triode 3| may be connected directly to the meter shunt, and the grid of triode 32 may be short-circulted, or connected directly to its filament leads.

By this means a very much smaller current may be measured, the triode 3| serves to amplify the input current sufliciently to change the plate current in the triode I by an amount great enough to give the desired scale reading upon the meter 5. Simultaneously the grid 82 produces enough change effect upon the grid of the triode 2 to compensate for any irregularities in plate voltage or filament current in the triode 3|. Co pensation for irregularities in power supply in triode I is thus efiected in the usual way and any irregularities of power supply in the amplifier triode 3i are similarly compensated for by the triode 32 in its effect on the triode 2. By this embodiment, values ranging from a R. M. S. value of 5 to millivolts are readily measured.

These embodiments are primarily adapted to the measurement of alternating current. They may however be utilized for the measurement of direct current by omitting the grid leaks and grid condensers, retaining the meter shunts. In such modifications, no rectifying or detecting action is necessary.

The device of my invention has been described as particularly applicable to the measurement of small values of alternating current voltage or amperage. It is likewise applicable to the meas urement of energy in terms of watts, which may be done by the system shown in Fig. '7. In this figure similar numbers represent similar members with the preceding figures, triodes I .and 2 being provided and also a power supply transformer 5, and an indicating meter 5, the transformer 5 having a primary I, a secondary 8, and

filament heating secondaries 23, 24, 25 and 26. Rectifier tubes 2i and 22 are provided and connected to the triodes I and 2 through filter choke inductances 2! and 28, with filter condensers-2d and 30. To this extent the embodiment is similar to the embodiment of Figs. 4 and 5. The

dliference lies in the grid circuits, identified as triode 2 is provided with two grid condensers and G8 which are similarly connected. Input transformers 49 and 50 are likewise provided. The input transformer 59 may desirably have a primary winding 5I which is adapted to be connected to the voltage of the supply which is under measurement. The input transformer 50' likewise has a primary 52 which may desirably be adapted to be connected with the current of the source which is under measurement. The transformer 49 is provided with two secondary windings 53 and 54 which are respectively connected to the grid circuits of the triodes I and 2, the secondary 53 being connected between filament circuit of the triode I and the grid condenser 45. A meter shunt 55 may be connected across the terminals of the secondary 53 if the energy delivered from the secondary is greater than can conveniently be handled by the triode I. The meter shunt 55 is however not an essential portion of the device of my invention. The secondary winding 54 is connected between the filament circuit of the triode 2 and the grid condenser 67. shunted if desired by a meter shunt 56. The transformer 50 likewise contains two secondary windings 58 and 59 which are also connected to the grid circuits of the triodes I and 2. The secondary 58 is connected between the filament circuit and the grid condenser 45 of the triode I. Itstermlnals may likewise be shunted by a meter shunt 50. The secondary 59 is connected between the filament circuit of the triode 2 and the grid condenser 48 of the triode 2. This secondary likewise may be shunted by a meter shunt 6|. It is to be noted that one of the secondaries is reversed in polarity with respect to the others in their connection to the triodes.

In the operation of this device the triodes are energized as previously described and the grid leaks l4 and I5 are adjusted to such values that in the absence of potential from the current under measurement, the meters 6 gives no indication. Upon the application of a potential, as to the coil 5I, equal potentials are impressed upon the grids of the triodes I and 2 through the grid condensers, the grid rectifying action occurs, and equal changes in current occur in both triodes, and therefore the meter 6 does not give an indication since there is no current flow through it. Likewise if current is impressed upon the primary 52 (in the absence of voltage upon the coil 5|) equal potentials are impressed upon the grids of the triodes I and 2, and as before, equal changes of current in the two triodes yield no meter reading. The simultaneous applica- Its terminals likewise may be I tion of potential to the grids corresponding to both voltage and current, however, prcducm a different situation. In the event that the current and voltage in the circuit under measurement are in phase, the potentials impressed upon the triode I by the primary 58 and the primary 53 are .in phase, and accordingly the potential impressed upon the grid of the triode I and therefore the change in the plate current is a summation of the effect of the two. At the same time, potentials are impressed upon the grid of the triode 2 through the condensers 41 and ll. But, due to the reversal of one of the coils in the transformers, these potentials are in phase opposition, 180 out of phase, and accordingly the eifect upon' the grid potential, and the plate current of the triode 2 is determined by the difference between the two potentials. The reading of the meter 6 is then proportional to the difference betweenthe sum and the diiference of the grid potentials, which diiference is proportional to the watts in the circuit.

It should be noted that care must be taken that the potential delivered by the reversed coil does not exceed the potential of the other coil connected to the triode 2, since if it does, an error appears. The meter reading is due to the spread between the sum and diflerence of the potentials derived from the current and voltage coils, which increases to the point at which the potential of the reversed coil exceeds that of the unreversed coil connected to the same triode. After this point is passed however no further increase in the spread occurs, as will be obvious. For commercial service in which the voltage is normally nearly constant this requirement is easily .provided for by reversing a coil in the voltage supply.

A The eflect upon the grid potential of two paralleled alternating current supplies is equivalent to that of one which is the vector sum of the two. Accordingly, in the above described device, the spread between the sum and diiference of the applied potentials decreases as the phase shift increases from zero displacement, and the meter reading decreases with the decrease in power present in a circuit of constant voltage and current, but increasing phase angle. Thus the meter reading indicates true watts, regardless of the phase displacement angle.

This system is well adapted to the usual commercial frequency power supplies. When used on such frequencies, it is however desirable for satisfactory operation that the grid condensers be of fairly large size, with values in the neighborhood of 1 mi. The system is also usable for the measurement of power present at higher frequencies, such as are found in the audio portions of broadcast systems. or for the measurement of the power input to loud speakers in determinations of the efficiencies of such devices. When so used, the grid condensers may be of the same size as recommended for the power frequencies, but are not necessarily of a size as large as this.

Another modification of the device of my inventlon may be used for the measurement of the volt-amperes present in a circuit. This em hodiment as shown in Fig. 8 may consist of triodes i and 2 as before, connected to a transformer I, having a primary winding I, a secondary winding 8, and auxiliary filament windings 2i and 25. A meter 8 as before is connected between the midpoint of the secondary 8 and the junction of plate to filament leads between the triodes i and 2. Rectifier tubes 2! and 22 are desirable, although not necessarily, provided and connected ix-ztween the terminals of the secondcry "3, and the triodes I and 2, and their filamerits supplied from auxiliary coils 26 in the transformer I. Filter chokes 21 and II and filter condensers 2! and II are also desirably provided as in the previous embodiment.

A similar grid condenser, grid leak, meter shunt and transformer system is also provided as in the previous t, the various corresponding parts being designated by the same reference numbers. The transformers I. and II are desirably provided with additional primary coils II and l! as shown.

The transformer 5 is also provided with an extra secondary I3, and an auxiliary filament heating secondary H, which are connected to a rectifier tube II, and filter system 18. These members supply energy to another triode ll, having a coupling cell it positioned in and between the plate and grid circuits. making it an oscillation generator at some convenient frequency, preferably within the so-called audio range.

A series of four addldonal triodes ll, it, it and 82 are provided as shown and their filaments suppliedlwith current from another auxlhsry secondary 83 in the transformer 8. Each of these triodes is provided with a grid leak 84 and grid condenser 88, and the triodes II and 82 are provided with direct connections between the grid I0 condensers and the filaments. The triodes l9 and BI are provided with. meter shunts or equivalent devices II and 81, one being adapted for use on a voltage supply and the other on a current supply. The plates of the triodes II, is, ll 35 circuit of the oscillator i1, which also has its a plate lead connected to the filaments of the four triodes.

In the operation of this embodiment to measure the volt-amperes in a circuit, at a phase displacement other than zero, as distinguished from watts at zero phase displacement, the respective filament and plate circuits may be energized by power applied to the primary 1 of the transformer I. The adjustment of the grid leaks I1 and I! may then be checked as before described. to make sure that the meter 8 reads zero when the oscillator]! is not operating. This oscillator may then he started, and the grid leaks El checked to assure that the meter 8 still stands at zero, thereby securing an equality of adjustment of the various leaks. The coils It and ii are connected in opposition as are the coils 52 and I2. Accordingly, with a proper adjustment of the respective grid leaks, the pulsating plate currents from the oscillator through the respective triodes and pairs of coils are equal, and neutralize each other's magnetization on the core. Thus no current is induced in the secondaries of the transformers I! and I, and no reading appears onthe meter-U.

This condition of balance is however disturbed by the application of a potential to either of the triodes 19 or II, as may be done by way of the associated meter shunts. grid condensers and grid leaks. The detector action reduces the current flowing in the trlode having the shunt, without change of the current in the emaciated trlode. A current corresponding to the diilerential current is then induced in the secondaries I! and SI, and applied equally to the triodes i and 2.

aisassa Being equal however, the change in current in these triodes is equal and no reading appears on the meter. When voltage and current potentials are applied to the respective triodes simultaneously, the primaries of both the transformers 49 and 50 are excited by differential currents, which induce currents in the secondaries. The induced currents are applied to the triodes I and 2 by means of direct and reversed coils as described for the watt-meter embodiment, and areading produced on the meter in the same way, to indicate the volt-amperes in the power circuit. The

volt-ampere meter is in effect a watt-meter in which means comprising the extra four triodes and the oscillation generator are provided for converting the phase displaced potentials, which it is desired to measure? for the volt-ampere value into proportionate currents having no phase displacement, which can vbe measured by a watt meter to give readings proportionate to the voltamperes. This system likewise provides for .complete compensation for any changes which may occur in the system from changes in the necessary power supply to the filaments and plates of the contained triodes.

It is of course obvious that the usual principles of compensation for temperature changes, etc., of good meter practice may be applied to these systems, including the use of manganin and like material for the shunts. and the balancing of various parts of the circuits against each other. Likewise the usual refinements of good meter practice may be applied to the meter 8, to obtain therein a suitable sensitivity, period.

'etc. I

The foregoing embodiments have been described as adapted to direct reading or indicating meters. It is not of course necessary that they be used only in such forms. The meter 6 may consist of a curve drawing or recording type, as well as the indicating type. It may also be of an integrating type, basically of the ampere-hour form, in which case, if the primary indication is of amperes, the integrated reading will be of ampere-hours, if of watts the reading will be watt-hours, and ifvolt-amperes, will be voltampere-hours.

The principle upon which my invention is based may be utilized for still other measurements by means of still other embodiments. It may be made to give a direct reading of the frequency in an alternating current circuit, either at commercial frequencies, or at audio or radio frequencies. In this embodiment, triodes i and 2 are provided as in'the previously described embodiments, and connected in series, as shown in Fig. 9. A power supply system, such as a transformer 5 having a primary winding 7, a secondary winding 8 having a mid-point tap, and auxiliary windings 9 and ill for filament heating is provided. A meter 6, as before described, is also provided and connected between the mid-point tap and the Junction lead connecting the filament circuit of the triode l to the plate of the triode 2, as shown. Grid condensers II and I2, and grid leaks i4 and ii are provided and connected in the usual way, as previously described.

The remainder of the grid circuits of the triodes may consist of the respective secondary coils SI and 92 of the transformers 93 and 94. The primary coils 95 and 9B ofthese transformers are connected in series, and to the source of the current the frequency of which is to be measured. The cores 9] and 98 of the transformers are made of iron in diflerent states of subdivisiomthe core 91 of the transformer 93 for instance being made of iron in a state of colloidal subdivision, and the core 98 of the transformer 95 being made of iron in a coarser state of subdivision, dependng on the range of frequencies which it is desired to measure.

' The core 97 may be made of a material prepared by dissolving and suspending ferric chloride in an ethereal solution of a suitable synthetic' resin, and reducing the iron to the metallic state in the presence of the resin. This may be done by a suitable reducing agent, which may be organic such as hydrochinon or hydrazine, or may be inorganic such as hydrogen, or other suitable means. The iron is kept in a colloidal suspension by the resin, and the ether and other solvents may be removed by evaporation, leav- 1118 a mixture of resin and colloidal iron which may be moulded into a body of the desired shape for a core in the usual way. For the measurement of'commercial frequencies the core 98 may be made of finely laminated sheet iron, stacked in the usual way. For the measurement of higher frequencies the core 88 may be made of pulverized iron of varying degreesof fineness, according to the frequency. It may be made of iron saturated with hydrogen and ground to a suitable fineness and then incorporated with a suitable proportion of resin, or it may be made by precipitating the iron fromsolution as the chloride in ether as for the core 91, but in the absence of the resin, and slowly, to permit a suitable growth of grain size, whereafter the resin may be incorporated, and the mixture moulded into the desired core shape.'

In the operation of this embodiment, the triodes compensate each other for variations of alternating current in the primary coils of the transformers 93 and 94. When however an alternating current is supplied to the primary terminals 99 and fiows in the primary coils 95 and 98 of the transformers 93 and 96, it induces currents in the secondaries 9| and 92. The current and voltage induced in the secondary OI depends practically entirely upon the current flowing in the primary, and because of the extremely fine state of subdivision of the iron in the core, and the virtual' absence of eddy currents, there is practically no change inthe transformer coupling with change of frequency, and no change of transformation ratio. The core 98 of the other transformer 94 being however of less finely divided iron, the eddy currents play a more important part in the ratio of transformation, causing it to vary according to the frequency.

The usual grid leak detector action occurs in the triodes I and 2, when the currents are induced in the secondary coils and applied to the grid circuits, resulting in a. change of conductance in the triodes. The same current flows in both primary coils, and the same magnetic induction is applied to both cores. One core transfers this inductive effect to its secondary coil practically without effect from change in frequency but the other transfers a variable induction according to the frequency of the supply circuit current. At a given frequency there will be a definite difference in the currents, and potentials, induced in the respective secondary coils, a definite difierence in the conductance of theassociated triodes produced thereby, and a definite reading on the meter. A change in the current under measurement, without change. in

.oi' the tetrodes I02 the frequency produces practically no change in the meter reading, since the relative ratio of transformation in the two transformers changes with a change in current to keep the actual difference between the potentials applied to the grids at a constant valve. .Anyv small error can moreover be compensated for by appropriate choice of the characteristics of the triodes, as well as by the usual compensation methods.

A change in frequency thus produces a change in the coupling ratio between the two transformers, and accordingly in the input to the triode grids, thereby giving a reading of the meter, which may be calibrated to read frequencydirectly. The meter may of course be an indicating instrument, or may be a recording or curve drawing one, according to the needs.

This embodiment is particularly adapted to radio frequencies, and particularly convenient in that field, because of the lack of convenient devices for indicatng directly the frequencies encountered in radio circuits.

By another embodiment it is possible to measure the phase displacement between currents of the same frequency. In this embodiment, illustrated in Fig. 10, a pair of tetrodes I 0| and I02 are provided, corresponding to the triodes I and 2 of the previously described embodiments. These are connected in series as before, and to a transformer 0 having a primary 1, secondary I, and auxiliary filament heating secondaries 0 and I0, for power supply as in the previously described devices. A meter 8 of the pattern previously described is provided and connected as before.

Thetetrodes. IM and I02 each containa niament, 9. plate and two grids. They may be of the usual type, now on the market, with the grids concentric, or they may be of a special type in which the grids are interposed between different parts of the filament and plate, coaxially positioned side by side rather than concentrically one around the other. The grids are each provided with grid condensers, the tetrode IOI having grid condensers I03 and I04, and the tetrode I02 having grid condensers I05 and I06. The grids of the tetrode IOI are connected together at a point between the tube and the condensers and are also connected to the lilament circuit through a grid leak I01. The grids are connected together at a point between the tube and the condensers and are also connected to the grid leaks I08 and I09, as shown, and by them to the filament circuit.

Input transformers are provided, which may be two in number as in the embodiment of Fig. 7, or may be four in number, as shown in Fig. 10. If four are chosen they may have or may omit an iron core, depending on the frequency of the connected circuit. In the embodiment shown, four transformers without iron cores are utilized. Current from one of the circuits under test is supplied to the terminals IIO, connected to the primaries of the transformers III and H2, and from the other circuit to be compared for synchronism or phase displacement. to the primaries of the transformers I I0 and I I 0.

The secondaries of the transformers III and II! are connected through the grid condensers to the grids of the tetrode IOI, together. The secondaries of the transformers H2 and IIB are separately connected to the grids of the tetrode I02 through the grid condensers I08 and I08.

In operation, the device of this embodiment receives potential from the two circuits-to be compared, and applies the two simultaneously to the two grids of the tetrodes. The comparison currents are applied together with the grids of the tetrode IOI through the transformers II I and H0, and the condensers I03 and I04, and, the grids being connected, the resultant potential is the vector sum of the two. The same potentials are separately applied to the grids of the tetrode I02 through the condensers I05 and I00, and consequently the cutest is that of the arithmetic sum of the two. If the two currents are in phase. the vector sum and the arithmetic sum are the same, the same change in conductance is produced in both tetrodes and no deflection of the meter occurs. If the currents are not'in phase the two sums produce the same change in conductance in the respective tetrodes, and a reading is obtained in the meter 0, which is a function of the phase difference only. The meter may accordingly be calibrated to indicate the phase diiference in any convenient terms.

are not the same. do not.

The above described functioning takes place at any frequency, commercial, audio, or radio.

,The above described synchronoscope or phase displacement meter is particularly adapted to use as amember of an aeroplane altitude meter.

The plane may be equipped with a short wavegenerator and radiator system, with a modulator adapted to modulate the output at a convenient lower frequency. A radio receiver is provided adapted to receive the short waves and demodulate them. A synchronoscope as above described is also provided, one of the comparison currents being derived directly from the modulator, and the other from the radio receiver. The modulation frequency may be chosen such'that the corresponding wave length is four times the maximum height which it is desired to indicate. The signal is radiated to the ground reflected, received and the modulation frequency of the received signal compared with the original frequency. The phase displacement between the two indicates the portion of a half wave of the modulation frequency reaching to the ground and back, and the modulation wave length being known, the actual height is indicated, and may be given by the calibration of the meter.

The construction of this device is shown in Fig. 11, in which the outline of an aeroplane is indicated with the apparatus required for the system shown diagrammatically. This may consist of a triode II! and associated oscillation generating circuits as show. An antenna II8, which may desirably be mounted in or on a wing, is supplied with current from the tank circuit of the generator and radiates the signal frequency. Auxiliary antennae IIO may be utilized for their directive properties, and, if the machine is a biplane, another auxiliary antenna may be mounted in the lower wing to serve as a wave channel, for the purpose of still further increasing the directive efl'ect to send the signal energy toward the ground.

A second triode I2 I, also equipped with oscillation producing circuits is connected with the triode II'I according to a suitable modulation system, here shown as the constant current sys- The triode Ill and its circuits are equipped to generate and radiate comparatively short waves, which may desirably be within the range of to 200 meters, according to the wave-length allocation. The triode I2! is adapted to gener- I triode i28 is provided, and such other amplifying equipment es may be desired may be included.

The synchronosoope device of the previously described embodiment is also a. part of the system, and is so shown, similar numbers indicating similar parts. Cine of the comparison frequencies derived directly from the modulator generator J23 by s coil 320, or similar device, connected to one pair of the meter transformers cs ill and H2. The other of the comparison frequencies is derived from the output of the detector triode and is supplied to the other pair of trans formers H and lit. I

Both the oscillator triodes and the detecto trlode mey be supplied with current from any convenient source, as batteries or a. suitable gem eretor. The meter tetrodes may also be supplied from batteries, etc, but a. convenient source'oi power is 2 direct current generator equipped with so armature having an actual electrical mid point in its winding, and 2. connection thereto through o. slip ring contact, the meter terminal being connected to the mid point. This serves as a. substitute for the previously described transformer construction, and dispenses with the rectifiers, since the rectificetion is obtained from the commutator. when such generator is included, it may also be used to supply the plate circuits of all the triodes, and by the addition of appropriate windings, which may be connected to slip rings, it may supply the filaments as well through transformers. It is also desirable that means be included for neutralizing the energy transferred directly from sender to receiver without passing to the ground f or reflection, but this means is not shown, since it is well known.

In the operation of this device, the two oscillation generators are energized, and radiate a modulated high frequency signal toward the ground. It is reflected at the ground, returned to the plane, and received. A comparison is then made between a. modulation frequency current derived directly from the generator and the modulation frequency which has been carried to the ground and back on a carrier frequency. If the plane is on the ground, there will be practically no phase displacement between the two. If the plane is in the air a. displacement will occur of a. magnitude proportional to the height above ground. This displacement will show on the meter, which may be calibrated to indicate the actual height above the ground. This system has the substantial advantage that it cannot give a. false indication to mislead the pilot, since it will give a reading only when all elements are functioning, and in the event of failure of any member, it reads zero, thereby warning the pilot that something is wrong, and that he cannot secure height readings from it. It may be noted also that all questions of phase relationships in the carrier frequency are without effect on the readings, since the carrier serves merely to transport the measuring frequency to the ground and book, and any changes in phase relation clue to reflection at the ground,

or influences in the radio circuits can only afiect the radio frequency, and cannot affect the measuring frequency.

The maximum altitude reading and the accuracy of measurement at low altitudes are interrelated, requirlng a. low maximum reading when accuracy at low altitudes is required. To avoid this limitation, the modulating oscillator may be provided with a plurality of interchangeable coils for various frequencies, or adjusting means, the adjustment being mechanically interlocked with an adjustable plural scale on the meter, so arranged that for high accuracy at low elevations a. comparatively high modulation frequency is used. Then when higher altitudes are reached, the frequency is reduced, and the scale changed to correspond.

Still another embodiment utilizing a similar system may be used for meter readings which require a high degree of amplification-such as thermo-couple measurements, especially in cases in which it is desired to operate a. contactor, or a rugged recording meter, or to control s, fuel feeding motor or damper directly from the thermo-couple indications. Tl'ris result may be obtained from the embodiment shown in Fig. 12. This is 2. system generally similar to those embodiments of my invention previously described, with adaptations to the special needs. It consists broadly of a. multi-stoge amplifier system, compensated for variations in the energizing power as before. and adapted to amplify the slow variations in potential of a pair of thermo-couples with change in temperature, to a. magnitude at l which they are of suflcient strength to operate devices such as those mentioned. It may be regarded as a. special resistance coupled amplifier in which there is practically no impedance, either inductance or capacitance, in the signal path, and a. minimum of resistance.

The device may consist of a series of pairs of triodes as shown in Fig. 12, whichmny be grad noted in size as indicated. They are then conhected with a. resistance network as shown, and may be energized from a transformer, rectifier, and filter system I3I as indicated, which may be of a. convenient or usual form, or may be replaced by any other convenient source of direct current of suitable voltage. The triodes I32 may convemently be or the type commercially Known as the 199. The triodes I33 may be of the type 112 or 171 type, and the trlodes I34 may be of the 250 type. If these types are used, the resistance I35 may be of approximately 7,888 ohms, the resistance I36 of 19,000 ohms, the resistance I31 of 1,904 ohms, the resistance I38 of 428 ohms, the resistance I39 of 1,370 ohms, the resistance I40 of 92 ohms, the resistance Ill of 9,000 ohms, and the resistance I42 of 40,000 ohms.

With an impressed voltage of 850 volts, each triode will then receive its normal current and voltage in the plate circuit. In addition, by the adjustment of the point of connection of the resistances MI and I42, the triodes I33 and I34 also receive the normal grid bias. The larger triodes, as those marked I33 and I34, desirably have their filament circuits energized by alternating current from auxiliary secondaries in the power transformer. Thetriodes I32 may have their filaments energized by power fromthe plate circuit as shown, since the current required is small, and less than the amount available from the plate supply circuit.

The input may be obtained from a pair of theroil mo-couples I43. inserted through the furnace or enclosure wall I44, preferably in a protecting tube.

I45. One of the thermo-couples is connected between the filament circuit and a grid In such a way that a rise in temperature causes it to make the grid positive, the other is connected between the filament circuit and the grid of the other triode of the pair in such. a way. as to make the grid fBeing. equal and oppositejn eachcase, however,

the changes in :current flow d o notFchange the total .current taken bythe system in the center .resist'ance network, nor doesone pair of triodes react upon another;

,fI'he change in current flow in the triodes I34 may be utilized in. any convenient way. A motor hating differentially wound fields as shown may be used, working against a spring, to perform any desired function in response to temperature changes, such as moving a pen on a chart, controlling a valve or damper, etc. Or the difierential windings may be superposed on the ordinary field winding of a standard type of motor. This motor may be utilized on a blower or in a similar way, and a first adjustment of speed may be made by adjustment of resistance in the usual field circuit; control regulation of the speed is then effected by changes in the currents in the differential field produced by the triode amplifier system. Alternatively a pair of plate resistances may be used, from which a voltage drop may be secured for any desired purpose, as well as many other modifications which will be obvious.

This arrangement gives a maximum current when the temperature is a maximum. This may be modified by changing the resistances I42 to such values that, at a regulated temperature, the currents in the triodes I32 are different by the amounts caused by the thermo-couple potentials on the grids, but the potentials applied to the second grids are equal. Under this condition, there is no difference of current flow in the triodes I33 and I34 at the regulated temperature, but a rise in temperature causes a change in current in one direction, while a fall causes a change in the other direction.

With base metal thermo-couples and substantial furnace temperatures, the potentials applied to the triodes I32 may be well up to their capacity, and the triodes I34 also may be used nearly to capacity, making available in their output circuits from five to fifteen watts of energy. With noble metal thermo-couples, or moderate furnace temperatures the potentials may be insufiicient to make optimum use of the triode capacities. In this case auxiliary resistances may be connected between the points a and b, and the points 0 and d, reducing the values of the resistances MI and increasing that of the resistances I42 so as to keep the potentials at the proper values. These auxiliary resistances give a. substantial reinforcing action and enable a relatively small potential difference upon the grids of the triodes I32 to effect a maximum change in the conductance of the triodes I34.

This amplifier system is responsive to current, or potential variations at any frequency, or to changes which occur at intervals or minutes or hours, since it has no inductive or capacitive reactance in the signal path. In addition It can be supplied with energizing current from a single transformer and rectifier system, without need for bias batteries or extra current supplies. For this reason It is particularly adapted to commercial thermo-couple measurements, as well as many other uses.

This system is also well adapted to use in the amplifying system of a radio receiver. It may, for instance, be connected as a full audio amplifier, the thermo-couples of the embodiment shown .in Fig. 12 being replaced by the'secondary coil of an audio frequency transformer supplied from a detector in the usual way. When so constructed, a high degree of amplification is obtainable over a wide range of frequencies. Alternatively the audio input may be derived from a resistance in the circuit of a rectifier, any steady current component being removed by the usual means.

A preferred embodiment, however, utilizes the first pair of triodes as detectors, as shown in Fig.

13. In this embodiment the pairs of triodes I32, I33 and I34 are provided as before, and the resistances I35 to I42inclusive. The thermo-couples I43 are however replaced by the coil and detector system shown. An additional resistance I46 having a resistance of ,50 ohms is connected in the main circuit between the filament leads and the power supply from the rectifier and filter, and provides a voltage of about 9 volts, suitable for grid bias in a detector triode, The coil I4I serves as input for the signal. One terminal of the coil I4! is connected to the negative endv of the resistance I46, and the other end to the grids of the triodes I32, going directly to one grid, and through a condenser I48 to the other. A grid leak I49 connnects the grid of the second triode to the filament circuit. The output from the triodes I34 may be supplied to a translating instrument, such as a loud speaker, in any convenient way, as through the transformer I50. Or, alternatively, a pair of plate resistances or inductances maybe included in the plate circuits of the triodes I34, in which case the energizing voltage may be raised by an amount to compensate for the'additional voltage drop, and the output device may be connected to the junctions between the plate leads and the resistances.

The radio signal may then be applied to the coil I41, and is by it supplied to the grids of the first pair of triodes. In one triode the so-called plate detection phenomena occur for the production of a detected signal which is an increased current with increase of radio frequency energy. In the other triode the grid circuit detection phenomena occur for the production of a signal which is a decrease in current with increase of radio frequency energy. These changes are thus in opposite directions. They are amplified by the following triodes as before and are combined at the output device or signal translator to produce a cumulative effect.

Cross connections may be utilized as in the thermo-couple device of the previous embodiment, for a substantial reinforcement of the signal strength, and since triodes in the first pair are small, the advantages of power detection are obtainable with a relatively small signal voltage. Also the system gives a superior fidelity of reproduction to any system previously used, since it contains no inductances or capacitances to produce resonance. It is a balanced system, which reduces the efiects of departure from rectilinearity of the characteristic curve of the triode, and neutralizes the resulting distortion. Even the distortion produced by the operation of detection is largely neutralized, since, while the fundamental modulation is repeated by the detectors as opposite changes of current, which are vice when used as an amplifier and detector, it is desirable that a high grade of radio signal be supplied to it. For this purpose the system shown in Fig. 13 is particularly desirable. It utilizes preferably the superhcterodyne principle, and includes a particularly eficient tuning means.

As shown in Fig. 13, an antenna 555 is connected to an oscillation transformer it? and a ground 35 The transformer secondary is connected to a detector triode i5 3 and is tuned by a variable condenser lu l in which the stationary plates are connected to the filament circuit and the movable plates are connected to the grid circuit. A grid condenser and grid leak are provided for a first detector or beat resolver and connested in the grid circuit of this triode. It. second triode its is provided and equipped as an oscillator as shown, with a tuning coil 3511 which is connected to and tuned by the condenser 355. This is accomplished by the provision of a second condenser section, with plates of a shape similar to that of the first section, but having a greater number, the movable plates being on the same shaft, and the stationary plates being in the same angular relationship as the first plates. The stationary plates of the second section are connected to the Junction between the grid of the triode I56 and the (2011 I51.

The two sections of the condenser are thus in series between the grid of the oscillator and the filament circuit; This series connection produces a variable condenser h h he" maller capacity at any given position than the capacity of the first section alone at the same position, and one which varies with it in strict proportion. The coils I51 and the secondary of the transformer I52 desirably also have inductances in the same ratio as the capacitances of the first condenser section and the whole condenser of two sections in series. This construction produces a pair of circuits which track and tune together, with a constant frequency difierence, regardless of the shape of the condenser plates. This is the requirement for a single control in a superheterodyne system, which is thus met in a very simple satisfactory way. In addition the first section of the condenser serves as the coupling means between the oscillator and the beat re.- solver, to combine the signal frequency and the local oscillations.

The intermediate or beat frequency from the first detector triode I54 is transferred to an amplifier system I58,.and the amplified signal may be supplied to the coil E59 and by it to the input coil Ml and the detector triodes.

Thissystem thus gives a particularly convenient single control for the superheterodyne system, since the accuracy of matching of the corn densers may bemuch lower to give equally good results. This is due to the fact that any deviations in the first section are effective in both circults, and any deviations in the second section are reduced in effect according to the size ratios.

The system is also applicable to a loop antenna, by matching the oscillator coil inductance in proper ratio to the loop inductance. Alternatively, a single coil may be used for both oscillator and beat resolver tuned circuits-by taking a tap at a suitable point for a part of the coil as tuning circuit for one triode, and the whole coil for tuning circuit for the other, the single condenser section being appropriately connected to the whole coil, and the series sections being connected to the portion ending at the tap.

Referring to Fig. 1%, the device of this invention may consist of a series of pairs of amplifier vacuum tubes as shown, which may be graduated in size and capacity as shown, and may be ener== glzecl from a suitable power source through a resistance network as indicated. The tubes l and 2 are output tubes and may desirably be triodes of substantial power capacity, according to the system requirements. The plates of these tubes are connected to the respective halves of the primary of an output transformer E3, the midpoint of the primary being connected to the power supply. The power supply l may conveniently be a rectifier, with a filter system, supplied through a transformer, from a source of commercial frequency alternating current, or may be any convenient source of power of suitable voltage and current capacity. The cathodes of the tubes l 2 are desirably supplied from the same power source, and should be connected together. The respective tubes and 2 and their connected transformer coils may, if desired, be shunted by a. resistor 23. This resistor may be omitted, if desired, but its presence supplies a small additional current through the remaining resistors and improves the stability of the system. If used, the resistor obviously should be of such a size as not to impose an undue current drain on the rectifier or to shunt an undue amount of current from tubes I and 2.

The second pair of tubes 5 and 6 likewise have their cathodes connected together, and may be supplied with power from a common source, which however must 'be insulated from the source which supplies the'tubes I and 2. Separate filament power secondary windings in the power supply transformer of the power source 4 are convenient and satisfactory means for filament or cathode heating power. The plates of the tubes 5 and 6 are also connected to the power source through resistances I and 8 and leads 9. The respective pairs of cathodes are connected by a ballast resistor II). This resistor is proportioned in value such that the voltage drop of the current of the tubes I and 2 flowing through it is equal to the desired voltage across the tubes 5 and Ii plus the grid bias, if any, on the grids of the tubes I and 2.

By this arrangement, the potential of the plates of the tubes 5 and 6 with respect to the tubes I and 2 is made that of the grids therein, and the plates of the tubes 5 and B may be connected directly to the grids of the tubes I and 2, as shown. The resistances '1 and 8 are then made i6 current flow through it, and

o the cell increasing the current of such size and value that the tubes I and I receive the normal current in the plate circuits. These values will of course be dependent upon the type of vacuum tube used in the respective I positions, and the power capacity.

It is of course obvious that the tubes I and I may be of the tetrode type. as well as of the triode type. and if such tetrodes are used, the screen voltage may be supplied in the same way as the plate voltage, by suitable resistors connected between the screen grids and the power supply. Tetrodes are particularly advantageous in this position, because of the high impedance into which they work, since the impedances of both the plate coupling resistors and of the grids of the following tubes are high.

A third pair of tubes areprovided as shown at H and I 2, which may desirably be tetrodes as.

indicated. The cathodes areconnected together as with the other pairs, and-to another insulated power supply, such as a third cathode heating secondary in the power system transformer. The plates are supplied with power from the same source as the others, through the lead I and the resistors II and i4, and a second ballast resistor i5 is provided, connected. between the cathode circuits of the tubes 5 and. and of the tubes II and i2. As before; this resistor is 01' such size and value that the voltage drop in it when carrying the plate currents of the tubes I, 2, I, and 6 will equal the voltage desired across the tubes II and I2, plus the grid bias, if any, on the grids of the tubes II and 12. The grids oi the tubes 5 and 8 are then connected respectively to the plates of the tubes II and I2, as shown.

This system is particularly convenient for amplifying the output of a lightsensitive cell, such as a photo-electric cell. For this purpose the cell it may have its cathode connected to the screen grid of one of the tubes, as tube It, and be supplied with power through the lead 9 and a resistor H, of such value as to provide the appropriate current in the cell, and the appropriate voltage drop. Fortunately, the desirable screen grid currents of suitable tetrodes are close to the desirable photo-cell current, and accordingly the two may conveniently be operated in series. The screen grid of the other tube of the pair is then supplied with current in parallel with the first, from the resistor II, which is calculated in size accordingly, through an auxiliary resistor l8 which is of a value approximately equal to the apparent impedance of the cell l6 under average conditions of illumination.

The grids of the tubes Ii and I! are then connected to the plate circuits of opposite tubes, of the pair 5 and 6, through resistors I9 and 2., as shown, and to the cathode circuit of the same I) pair through resistors 2| and 22. As before, the

bias, if any, on the grids of the tubes II and i2 is controlled by the proportioning of the resistors.

In the operation of this invention, changes in the light incident upon the cell l6 change the the current flow to the screen grid of the tube It. Simultaneously, a change in current in the cell produces a similar and opposite change in current in the screen of the tube ll; an increase in illumination on to the tube l2, and reducing the current to the tube ll. These changes in current tend to produce current changes in the plate circuits oi. the tubes, but because of the constant current characteristics of the tubes produced by the plate coupling reto the grids of the tubes I sistors, voltage change: are produced instead in the plate circuits. which are applied to the grids oi the successive cascade tubes, for amplification therein in the .usual way.

Thus a voltage change circuit of the tubes 8 and 0. is returned in part through to the control grids of the tubes Ii and ii, to produce a substantial and valuable reinforcing action, the steady current component being passed to the cathode circuit through the resistors 2| and 22, to set the potential of the grids.

Another portion of the voltage change in the plate circuits of the tubes 5 and 8 is applied and 2. to produce current changes therein of substantial value, which are delivered by the output transformer I to the loud speaker, or other work circuit.

A change in illumination on the cell thus produces a change of current therein, which is applied to the screen grids of a pair of tetrodes, to produce an amplified voltage change in the plate circuits thereof of opposite phase, and substantially equal value. These changes are further amplified, and retumed in part for a further reinforcing eflect. Another portion of the amplified voltagesare further amplified and used to control the current in a translating device.

It may be noted that there is substantially no impedance in the signal path in this amplifier appears in the plate This voltage change except that of the tubes themselves, so there is a minimum of frequency discrimination in the circuit. Likewise, because of the balanced character of the pairs 01' tubes, the current in the ballast resistors tends to remain constant, thereby preventing undesired reaction efl'ects which may tend to make the system unstable. Instead, the presence of the ballast resistors tends strongly to stabilize and equalize the currents in the respective tubes of each pair, since any departure from 4 a condition of equal and opposite current change tends to change the current in the resistor, which change is opposed and the tendency corrected.

This tendency makes it possible to operate this amplifier without bias upon the grids of the amplifier tubes, since the departure from proportionality caused by the grid current during the positive swings is compensated and neutralized by this correcting tendency. Furthermore, the symmetrical character of the entire system permits of a substantial departure from exact equality of amplification of the positive and negative swings upon the grids, since the departure of one tube from maximum on one half cycle is balanced by the same departure by the other tube of the pair on the next half cycle.

In consequence, while maximum fidelity of amplification is obtained by the use of suitable bias on the grids of the respective tubes, the system may be operated without grid bias for a substantial saving of supply voltage, at the cost of only a small reduction in fidelity, and a small-reduction in power output.

The method of coupling the light sensitive cell to the amplifier system is also particularly advantageous, since it gives equal and opposite impulses to the associated amplifier tubes from a single cell, and there is no frequency modifying impedance in the cell circuit to limit the range of frequency response. Instead, the cell and the whole amplifier system to the output transformer are free from limits on the low frequency end, and are limited only by the characteristics of the resistors I! and 1e tubes and the small parasitic circuit caa change in the potential of the junction point icitances at the high frequency end. The limit herwise imposed by the output transformer ay be removed by substituting for the transrmer a pair of output resistances as will be ivious, at a cost however of increased supply :ltage.

The remaining portions of the circuit are self- :planatory, the return lead to the power source sing connected to the cathode circuit of the Lbes H and I2, and if desired, a small additional illast resistor may be connected in parallel with re tubes l and 2, as shown at 23.

The method shown above for connecting a ght-sensitive cell to an amplifier system is parcularly advantageous for the amplifier system iown. A similar type of connection may howrer be used between a cell and a single tube as iown in Fig. 15. In this arrangement, a tetrode lbe Si is provided, together with, appropriate late and cathode power supplies as shown. The all 32 is connected directly between the screen rid of the tetrode, and an appropriate voltage aint on the plate power supply, the screen grid irrent thereby being used to energise the cell, before outlined. Under proper conditions as ith a suitably designed tube the control grid f the tube may be left free, and unconnected ith other parts of the circuit. Most tubes will owever require that the grid voltage be set, 'hich may be done by connecting it directly to re cathode circuit, or through a resistance 33. he amplified output may be transferred through :1 output transformer 34 to the desired load ciruit, such as an additional amplifier stage.

In a grid resistor 33 is used, a greater output my be secured by the use of a cross connection etween plate and grid, which may consist of a Jndenser 35 arid resistance 36, as shown.

Alternatively. the circuit of Fig. 16 may be sed. In this circuit the tube 4| is equipped 'ith power supplies in the usual way, and the ell 42 is connected in the screen grid circuit as efore, but in series with a resistor 53. The ontrol grid is connected by a resistor 34 to the athode circuit, and through a condenser 45 to he junction point between the cell 42 and reistor 43. An output transformer 46 is connected '1 the plate circuit in the usual way.

In the operation of the device of Fig. 15, a hange of illumination on the cell 32 causes a hange of current to the screen grid of the tube I, which is amplified in the usual way in the utput circuit. When the condenser 35 and relstor 36 are used, a portion of the amplified curent in the plate circuit is returned to the conrol grid, to cause a still further degree of amlification. It may be noted that this seems to e a new method of reinforcing signals, since the hange produced in a plate circuit by one grid is upplied to another grid, as in the standard amilification system, but the second grid is in the ame electron stream as the first. Also, by makrig both the condenser 35 and resistor 36 of good ize, the impedance of the condenser becomes iegligible, and the adjustment of the resistor letermines the amount of amplification.

In the operation of the device of Fig. 16, a hange of illumination on the cell 42 changes he current flowing in the screen grid circuit, and hrough the resistor 43, thereby changing the .urrent in the plate circuit, to produce an amlified output in the plate circuit and the asociated transformer 46. Simultaneously, the hange in current in the screen grid circuit causes between the cell and the resistor 43, which change is transferred through the condenser 45 to the control grid of the tube. This change in potential is in the proper phase to accentuate the change in the electron stream by its effect on the control grid, thereby giving a greatly increased output from the amplifier tube. It may be noted that in both of these circuits there occur condensers which impose a lower limit on the translatable frequencies. This limit is however close to the lower limit of audibility because of the small efiective impedance of the condenser compared to the resistance of the resistors in series with it. However, this limit is not an absolute one, but merely a limit at which the added amplification ceases to be effective, the original efiect of the cell on the tube being independent of frequency.

The devices of this invention thus providea new and efifective amplifier system, adapted to operate with or without. grid bias, and a new system of coupling circuits for light sensitive cells to amplifiers, both of which are especially adapted to the translation of a wide range of frequencies, and to a high efllciency of operation.

While there are above described but a limited number of embodiments of the device of this invention, it is possible to produce still other embodiments of the inventive concept in accordance with the spirit disclosed, and it is accordingly desired that only such limitations be imposed on the appended claims as are stated therein, or required by the prior art.

The invention claimed is: I

1. In combination a light sensitive cell and an amplifier system comprising a plurality of pairs of vacuum tube amplifier devices, and circuits therebetween to cause said devices to be connected in balanced cascade relationship. the input pair thereof being tetrodes, direct metallic connections between said cell and a screen grid of one of said tetrodes and a balast resistance, the screen grid of the other of said'tetrodes being connected to said ballast resistance through a resistance in parallel to said cell.

2. In combination, a pair of balanced amplifier tubes, balancing circuits and connections-there- ,for, a light sensitive cell connected thereto, and connections from a positively biased grid in one of said tubes to said cell and from a positively biased grid in the other of said tubes through a ballast resistance to said cell.

3. In combination, a light sensitive cell and an amplifier system associated therewith and comprising a tetrode amplifier tube and a direct metallic connection between the scren grid ofthe tetrode and the cathode of the photocell, there being no other direct metallic connections to either the screen grid or the photocell cathode.

4. In combination, a light sensitive cell and an amplifier system comprising a tetrode and a single connection to the screen grid thereof leading to the cathode of the photocell only, whereby the photocell cathode is in direct metallic connection only with the screen grid of the tetrode and a grid leak and grid condenser connected to the control grid of said tetrode.

5. In combination, a light sensitve cell and an amplifier vacuum tube having an anode and an anode circuit for output'therefrom, a cathode and a plurality of grids, and a series circuit connecting one of said grids to the cathode of said cell for supplying electrical energy thereto, said v grid being at a positive potential with respect to 

